Integrated circuits and chips have become increasingly complex, with the speed and capacity of chips doubling about every eighteen months. This increase has resulted from advances in design software, fabrication technology, semiconductor materials, and chip design. The increased density of transistors per square centimeter and faster clock speeds, however, make it increasingly difficult to specify and design a chip that performs as actually specified. Unanticipated and sometimes subtle interactions between the transistors and other electronic structures may adversely affect the performance of the circuit. These difficulties increase the expense and risk of designing and fabricating chips, especially those that are custom designed for a specific application. The demand for complex custom-designed chips increases with the burgeoning number and variety of microprocessor-driven applications and products yet the time and money required to design chips have become a bottleneck bringing these products to market. Without an assured successful outcome within a specified time, the risks have risen along with costs, and the result is that fewer organizations are willing to attempt the design and manufacture of custom chips.
Without a doubt, integrated circuits must communicate with one another. Most communication data between computers is digital data, meaning that the information content is contained in the series of “0”s and “1”s represented by different voltage levels of the signals. Where once stand-alone desktop computers were the norm, now networked computers are the standard of efficiency since the Internet has fueled the exponential growth of the communicating information, especially in the medical, entertainment, teleworking, and consumer fields. One model of communication between devices over an electronic network is the open system interconnection (OSI) model having seven layers between stations; these layers are referred to as protocol layers. Control is passed from one protocol layer to the next, starting at the application layer in one station, proceeding to the bottom or physical layer, over the channel to the next station and back up the hierarchy to the application layer.
The bottom layer is the physical layer, the PHY, that conveys the bit stream, i.e., the electrical impulses, light or radio signals at the electrical and mechanical level. The PHY is the hardware for sending and receiving data and includes the transceiver. In some models, the PHY may have three components: (1) one which encodes and decodes the data stream to and from the upper layers; (2) another which serializes coded groups into bit streams and then deserializes the receiving bit streams into code groups; and (3) the actual electronics for signal transmission including the amplification, modulation, wave shaping, and transmission. There is a whole spectrum of PHYs and respective transceivers dedicated to the exchange of electronic and optical data through networks and/or within computers or other microprocessor-driven devices. The physical parameters that determine what PHY is appropriate for what network and what data includes whether the data is optical or electrical, digital or analog, the frequency of the data, the attenuation and the bandwidth of the exchange medium, the impedance, the signal voltages, and other electrical characteristics of the electronics on either side of the transmission medium, etc. Bandwidth is simply how much digital data, whether it be voice, text, or video data, can be sent through a connection. As examples, cellular telephones are low bandwidth and the transmission medium is air whereas cable television is high bandwidth using fiber optics as a transmission medium. Broadband refers to the transmission rates needed to simultaneously receive voice, data, graphics and multimedia applications and are measured by how many bits of data can cross the wire each second. Slower transmission speeds are measured in kilobits per second (Kbps), while faster transmissions are in megabits per second (Mbps) or gigabits per second (Gbps). At these high transmission rates, the medium can be fiber optics and/or copper wire. An example of one kind of PHY embodies full duplex, point-to-point communications channel for gigabit speed serial interfaces that is independent of the protocol and may be independent of the media. These interfaces are compatible with storage subsystems, network switches and routers, storage area networks, and high-speed backplanes. Another type of PHY may be an optoelectronic interconnect for broadband and networking applications for extremely high bandwidth CMOS ASICs. Ethernet, Fibre Channel, SONET/SDH, Serial ATA, and ATM are examples of protocols requiring specialized PHY layers. The PHY is connected to the next protocol layer, the data link layer, in which data packets are encoded and decoded into bits. The data link layer has knowledge of the transmission protocol, manages errors in the PHY, flow control, and frame synchronization. The data link layer is divided into two sublayers: (a) the media access control (MAC) layer and the logical link control (LLC) layer. The MAC sublayer controls how to access the data and gains permission to transmit the data. The LLC layer controls frame synchronization, flow control and error checking. There are a variety of MACs that support copper and optical fiber networks at data transmission speeds ranging from 10 to 1000 Megabits per second (Mbps) on a single platform to many gigabits per second (Gbps).
The next protocol layer beyond the data layer is the network layer that provides switching and routing technologies, creating logical paths for transmitting data from node to node, or from server to server. Addressing, internetworking, error handling, congestion control and packet sequencing are also functions of the network layer. The transport layer is the protocol layer after the network layer and provides transparent transfer of data between end systems or hosts, and is responsible for end-to-end error recovery, flow control, and ensures complete data transfer. The fifth protocol layer, the session layer, establishes, manages and terminates the conversations, exchanges, and dialogues between the applications at each end, and deals with session and connection coordination. The next protocol layer, the presentation layer, provides independence from differences in data representation, e.g., encryption, by translating from application to network format, and vice versa. The presentation layer works to transform data into the form that the application layer can accept by, for example, formatting and encrypting data, to be sent across a network. The presentation layer provides freedom from compatibility problems and is sometimes called the syntax layer. The application layer is the last protocol layer and supports end-user processes. Communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. The application layer provides services for file transfers, e-mail, and other network software services. Telnet and FTP are applications that exist entirely in the application level. The OSI model is only one model and is nothing more than a conceptual guideline. The actual layers are not easily categorized. There may be, for instance, an overlap or even differences between the functions of the different protocol layers than as described above.
The convergence of systems used in the local area network (LAN), wide area network (WAN), metro area network (MAN), and storage area network (SAN) environments requires new interoperable communications technologies to support multiple protocols, including, e.g., Ethernet for the LAN, SONET/SDH (synchronous optical network/synchronous digital hierarchy) for the MAN/WAN, and Fibre Channel for the SAN. Several digital data communication standards have facilitated the growth of the communications industry, and one such standard having the capability for broadband, gigabit, low voltage communications is the System Packet Interface Level 4, Phase 2 (SPI4-2) that defines the MAC and PHY layers for a network for devices in close proximity. Originally designed for packet and cell transfer between a MAC device and an ASIC, network processor unit (NPU), or switch fabric, SPI4-2 supports the transmission of multiple communications protocols up to 10 Gbps including Packet over SONET/SDH (POS), OC-192, 10/100/1000 Ethernet, 10 GbE, and 10G SAN By providing a common interface for 10 Gbps WAN, LAN, MAN and SAN technologies, SPI4-2 is ideal for systems that aggregate multiple low-data rate channels into a single 10 Gbps uplink for long-haul or backbone transmission.
Another standard is the 10 Gigabit Ethernet standard that extends Ethernet applications to operating speeds of 10 Gbps and still be compatible with older, slower Ethernet protocols. The 10 Gigabit Ethernet standard is full-duplex and uses fiber optics, thus extending the speed and capability of Ethernet. The XAUI (pronounced zow' ee) for 10 gigabit attachment unit interface, is an Ethernet-only specification (IEEE802.3ae), defined for MAC to PHY connections in 10G Ethernet systems, unlike SPI4-2 which is a suitable system-level interface for point-to-point connections between MACs and NPUs or switch fabric devices.
Typically high speed interfaces are differential, meaning that the data is encoded in a voltage between the normal digital high voltage of one volt as a “1” and the normal digital low voltage of 0 volts as a “0”. A differential voltage enables faster data transfer rates because of smaller voltage transitions. There are several high speed serial interfaces, and, ranked in approximate order of speed from slowest to fastest, they are: emitter coupled logic (ECL), positive emitter-coupled logic (PECL), low voltage differential signaling (LVDS), and current mode logic (CML). ECL is the traditional high-speed logic technology, originally based on bipolar transistor differential pairs with a negative bias supply. PECL is a form of ECL referenced to a positive bias. ECL devices have propagation delays in the region of 200 picoseconds and toggle frequencies over 3GHz. Of all the interfaces available today, CML swings at about one-half volt and operates at the highest speed and is used in applications requiring gigabit data rates. LVDS is a low noise, low power, low amplitude method for data transmission over copper wire at the gigabits per second range. Low voltage means that, in accordance with an industry standard, the differential signals have an amplitude ranging from 250 millivolts to 400 millivolts at an offset of 1.2 volts. LVDS uses a dual wire system running 180 degrees of each other so that noise is filtered easily and effectively. ECL and PECL transmitter-output signal swings are higher and the propagation delays are shorter than those of LVDS transmitters, thus ECL and PECL devices dissipate power and thus heat more.
Because there are so many variations in the applications, the data, the speeds, and standards, it becomes expensive and burdensome to design and manufacture individual full custom chips for specific applications and protocols. Thus, there is a need in the industry to accommodate desired flexibility and variety available in high speed digital communications. In addition, developers need off-the-shelf building blocks to design these multisystem solutions to save time and engineering resources.